One Universe at a Time

Hidden In Plain Sight

A new dwarf galaxy has been discovered in the constellation Crater. It is the fourth largest dwarf galaxy orbiting our Milky Way, and it’s only 390,000 light years away. So why wasn’t it discovered before? Because it was hidden in plain sight.

The galaxy, known as Crater 2, has two characteristics that make it difficult to observe: it’s diffuse and faint. While we can easily detect stars that are part of the galaxy, recognizing that the stars are part of Crater 2 rather than our own galaxy is rather difficult. To discover it, a team of astronomers analyzed data from the VLT survey telescope, finding a statistical fluctuation in the apparent density of stars in the region. It’s the size of this dwarf galaxy that made it statistically stand out. There could be similar dwarf galaxies orbiting the Milky Way that are just waiting to be discovered.

What’s interesting about Crater 2 is that it seems to be part of a cluster of dwarf galaxies. Members of this Crater-Leo cluster seem to be gravitationally coming together. It just goes to show that even though we’re now able to observe some of the farthest reaches of our Universe, there are still things waiting to be discovered in our cosmic back yard.

Paper: G. Torrealba, et al. The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater. arXiv:1601.07178 [astro-ph.GA]